Not applicable.
Not applicable.
This invention relates generally to chair control mechanisms, and more particularly to a spring assembly for a chair tilt control mechanism.
Task chairs or office type chairs have evolved greatly over the years to improve the support provided to chair occupants and to provide chairs that better meet the usage needs of modem chair users. Comfort and promotion of ergonomically healthy sitting are among factors considered by occupants when choosing a chair. The development of backrest tilt control mechanisms has enabled chair occupants to adjust the backrest of a chair to their preferred positioning.
The spring assemblies associated with chair tilt control mechanisms allow occupants to recline the backrest, and also operate to bias the chair to its upright position when the reclining force is relieved. The spring assemblies are an important component in providing comfort to the user. To allow the users to adjust the chair properly, it is desirable to allow adjustments of the force needed to recline the chair and the force with which the chair returns to an upright position.
It is also desirable that more force be necessary in reclining the backrest of the chair than when resisting the biasing force on the backrest that returns it to an upright position. The difference in these forces is termed xe2x80x9cdwell.xe2x80x9d Dwell is important in meeting the needs of most chair users. With the dwell properly balanced, a user can recline the chair to a desired position and maintain that reclined position with very little effort. Ideally, the mechanism is adjustable so that the weight of the user""s upper body balances the chair in the reclined position.
Rubber torsion springs have traditionally been used in the spring assemblies of tilt control mechanisms to achieve the desired dwell in the action of the backrest. In use, the rubber springs are mounted to a rod and energy is stored within the rubber springs as the backrest is reclined. But rubber springs have a limited life due to the inherent limitations of the material. For example, the rubber can break after a long period of use, or the spring characteristics can shift as the rubber ages. Additionally, even new rubber springs can vary due to batch differences in the base rubber material. A mechanism is needed that achieves the desired dwell in the action of the backrest, without the disadvantages of rubber springs.
This invention is directed to a steel spring assembly for creating dwell when returning the backrest of a chair to an upright position from a reclined position.
In one embodiment, the invention provides a spring assembly for use in a chair tilt control mechanism. The tilt control mechanism is one that can recline and return a backrest for a chair. The spring assembly includes a cylindrical block that has first and second ends and a central bore. A pair of end caps is located at each of the first and second ends of the block. Each end cap has a receiving section that can rotate within the central bore of the block. Each end cap also has a hole extending through it that provides a coupling point for the chair backrest. The spring assembly also includes at least one steel coil spring around the block. Each spring has one terminal end coupled to the tilt control mechanism and the other end coupled to one of the end caps. The end caps rotate within the block as the chair backrest is reclined or returned. The force needed to rotate the end caps is a sum of the spring force provided by the spring and the frictional relationship between the block and the end caps.
In another embodiment the spring assembly further includes a bearing located within the central bore that can rotate within the central bore of the block. Each end cap has a truncated receiving section that can rotate within the central bore of the block. The bearing and end caps rotate within the block as the chair backrest is reclined or returned.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.